I thought in years gone by it was 2% for Visa, MC and Discover to the merchant and more like 3% or even 4% for AmEx which is why so many don’t accept it.
Not sure what the %’s are in 2015.
That could be.....I think the main thing is that AMEX was always higher than the rest.
These days, a small merchant can use Square:
Square's Payment Processing Fees and Pricing
It's 2.75% for swiped cards and online transactions (via their online portal). Period. No signup fees, no per-transaction fee. Manually-entered transactions are 3.5% + 15 cents.
And they accept most cards:
You need an iPhone or Android phone, and Square's reader. Their mag-stripe reader is free, and their combination stripe/chip/contactless card reader will be $49, once it is available.